<VV> Fuel mileage and the cold

[Mikeamauro at aol.com]

:.. once warmed up, the cold air results in a denser  charge, great for 
power, not so great for mileage..."
 
Maybe, maybe not; depends on how lean the AF ratio goes. Read from my  
earlier post:
 
 
(after speaking about effect of  cold weather "choked"  operation) Now, 
about the effect of cold weather on air-fuel mixture... colder  air is denser 
(this means, for an engine, at a given elevation, more oxygen  to work with). 
Therefore, with a carbureted engine (after the chokes are  fully open), as 
the air temperature falls, the AF ratio increases (the mixture  becomes 
leaner). For example, my 67 coupe is equipped with wide band O2  sensors and 
digital AF gages in the cabin... in the summer the AF ratio, at  cruse, is 
consistently 14.5 to 15.5:1. Now, with the air  temperature primarily below 
60-degrees, it is not unusual to see AF ratios  above 16:1 at cruse. When I get 
into the petal, as I'm using the later, before  smog, fuel enrichment carbs, 
the ratio drops to a safe range  for acceleration (but that's another 
topic).     With  colder meaning leaner, one would think colder would 
automatically mean better  fuel mileage... maybe, and this is purely theoretical-speak: 
there is a  point for any engine-vehicle combination where a too lean 
condition (besides  causing engine damage) can cause efficiency to "fall" off the 
 performance curve. Finding and holding the "sweet spot" with a carbureted 
engine  is a challenge; hence, precisely the reason fuel 
injection--especially the  modern, microprocessor-controlled version--was  developed.     


Mike Mauro
of several Corvairs  http://community.webshots.com/user/mikeamauro